The present invention relates to pools made of plastic side walls and a plastic bottom liner. Such liners usually include a peripheral bead around the top edge thereof which is inserted into a groove in the pool plastic side wall.
Some manufactures mold the groove into the plastic side wall wherein the groove is defined entirely by the plastic material of which the side wall is made. The problem with this approach is that tolerances are difficult to maintain and accordingly, the liner often falls out of the groove during the life of the pool.
To overcome this, some artisans embed a metal channel in the plastic pool wall such that the metal channel defines the groove and close tolerances can be maintained. Where the groove is located above the water line, such an approach is fairly satisfactory.
However, many people prefer pool constructions wherein the plastic side walls are completely exposed and only the bottom of the pool is covered by a plastic liner. In such a case, the bead receiving groove and embedded metal channel in the plastic side wall have to be located towards the bottom of the plastic side wall below the waterline. Because of the differential expansion and contraction of the metal and plastic, and/or because of the difficulty of getting a good seal between the channel and the pool wall, water can leak around the upper channel wall and from thence all the way around the metal channel and into the space between the plastic wall and liner. This can cause errosion of the foundation of the pool, particularly where the bottom is merely sand, rather than concrete. It can cause unsightly bulges in the plastic pool bottom liner which may eventually lead to damage of the bulging portions. Finally, it can cause a nagging loss of water from the pool.
In my prior U.S. Pat. No. 3,975,782, I conceived a method for solving this problem which involved providing the plastic liner with a first bead for fitting into a metal channel groove in the pool side wall and a second bead located there above and joined thereto by an intervening flap. The second bead would be fitted into a plastic groove molded directly into the pool wall. The first bead and metal groove served to hold the bulk of the weight of the plastic pool liner while the second bead and plastic groove can be grouted to prevent water from leaking in behind the flap and metal channel. Because the upper groove is plastic, there is no expansion or contraction problem of the type encountered where the groove is defined by a metal channel.
While this prooved to be a satisfactory solution to the problem, it was not acceptable in all instances in that, even with most of the load being carried by the metal channel groove, a tolerance problem in the upper groove still allowed the upper flap to fall out of the groove from time to time.